|
||
By
From the Immunology Research Group, Biological Sciences, University of Manchester, Manchester
M13 9PT, United Kingdom
The cellular basis of immunological memory remains a controversial area with respect to the
identity of memory T cells and the role of persisting antigen. CD4 T cells are phenotypically divided by the expression of high and low molecular weight isoforms of CD45, surface markers
that are frequently used to identify "naive" (CD45Rhigh) and "memory" (CD45Rlow) subsets.
The latter subset responds rapidly in antigen recall assays but paradoxically has a short life span,
a property that is difficult to reconcile with long-term memory. The present study examines
these issues using a DTH (delayed-type hypersensitivity) model in which contact sensitivity to
dinitrochlorobenzene (DNCB) was transferred to athymic nude rats by recirculating CD4 T cell subsets defined in the rat by the anti-CD45RC mAb OX22. As expected, CD45RC+ (but not
RC
) CD4 T cells from normal unprimed rats transferred a DNCB-specific DTH response,
whereas, 4 d after sensitization the CD45RC
(memory) subset alone contained the DNCB
reactivity. However, when donor cells were collected from thymectomized rats sensitized two
mo earlier, DNCB-specific responses were transferred by both CD45RC
and RC+ subsets
suggesting that many of the latter had developed from cells with a memory phenotype. This
was confirmed when CD45RC
CD4 T cells from 4-d primed rats were parked in intermediate nude recipients and recovered 2 mo later. DNCB-specific activity was now found wholly
within the CD45RC+ "revertant" subset; the CD45RC
CD4 T cell population was devoid
of activity. Importantly, we found that the total switch-back from CD45RC
to RC+ could
be prevented, apparently by persisting antigen. The results indicate that there are two functionally distinct categories of memory T cells: one, a short-lived CD45Rlow type which orchestrates
the rapid kinetics, the other, a longer-lived CD45Rhigh revertant which ensures that immunological memory endures.
This article has been cited by other articles:
| TABLE OF CONTENTS |
|